Electrochemical method for cleaning the surfaces of metallic work pieces and cleaning electrode

ABSTRACT

The invention relates to an electrochemical method for the cleaning surfaces of metallic work pieces and an electrode ( 1 ) for the electrochemical cleaning of surfaces of metallic work pieces ( 2 ), especially surfaces in the region of welded seams. The electrode comprises a connection ( 4 ) enabling it to be connected to an electric voltage source ( 5 ), and an insulating layer ( 7 ) for the impregnation of an electrolyte ( 8 ). The aim of the invention is to improve the cleaning effect and to accelerate the cleaning process and to provide maximum protection for an electrode ( 1 ). A device ( 9 ) for generating an oscillation, especially an ultra sound transmitter, is provided in or on the electrode ( 1 ).

The invention relates to an electro-chemical method for cleaning thesurfaces of metallic work pieces, in particular the surfaces in theregion of welded seams, by using an electrode, wherein an insulatinglayer is arranged between the electrode and the work piece, and avoltage is applied between the work piece and the electrode and theinsulating layer is impregnated with an electrolyte.

The invention further relates to an electrode for electro-chemicallycleaning the surfaces of metallic work pieces, in particular thesurfaces in the region of welded seams, with a connecting terminal forconnection to an electric voltage source and an insulating layer to beimpregnated with an electrolyte.

While being processed, metal surfaces often become contaminated which,however, should be avoided both for reasons of corrosion and foraesthetic reasons. Problems are mainly posed by contaminations occurringduring the welding of metal construction parts on account of the heatoccurring during the welding procedure. These are oxide layers, slags orother welding residues which cannot be completely prevented even inwelding procedures under a protective gas atmosphere.

To remove such contaminations, the work pieces often are cleaned in aseparate working step which may be by mechanical action, chemicalmethods or electro-chemical methods. Purely mechanical cleaning methodsoften are very complex and lead to undesired scratches also on thosesurfaces which had not been contaminated. However, such scratchedsurface areas in turn are characterized by being increasinglysusceptible to corrosion, frequently requiring a furtherafter-treatment. Gentler, yet not as effective, are chemical methods(e.g. pickling), in which the contaminations are removed with certainsolvents.

Optimum cleaning results, particularly in case of contaminations whichoccur after the welding processes on the metal surfaces, have beenobtained by electro-chemical cleaning methods in which thecontaminations can be quickly and gently removed by forming anelectro-chemical cell or an electrolysis cell with simultaneousmechanical action. In doing so, the work piece to be cleaned isconnected to the pole of a voltage source while the electrode (cleaningelectrode) is connected to the other pole of the voltage source. Theelectrode is provided with an insulating layer so that a short circuitbetween the work piece and the electrode can be produced. To form anelectro-chemical cell or an electrolysis cell, the insulating layerwhich, as a rule, consists of a fabric, e.g. a fiberglass fabric, isimpregnated with a liquid electrolyte. By the action of the electrolyteand the electric current, the surface of the work piece is galvanicallycleaned in the region between the electrode and the work piece surfacelocated therebelow. The electrolyte may be manually applied to theinsulating layer of the electrode, or it may be continuously guided tothe electrode by a respective feed line.

DE 200 19 118 U1 describes an apparatus for the localized cleaning ofmetal surfaces, particularly in the region of welded seams, comprising acell of a corrosion-resistant material, by which a spent pickling acidis held back in the working position. To improve the cleaning effect,pickling acid present in the interior of this cell is set intovibrations. For this purpose, a generator for ultrasonic waves is putonto the end of the sonotrode. Apart from the fact that the use of suchacids for pickling the metal surface requires special precautions, alsothe construction of the cleaning device is particularly laborious andcomplicated. Moreover, sealing relative to the surface to be cleanedoften is difficult, or not possible, respectively, because of theroughness of the surface.

A device for electro-chemically cleaning metal surfaces of this type isdescribed, e.g., in DE 298 23 753 U1. There, a combination of amicro-abrasive treatment and an electro-chemical treatment is describedfor as effective a removal of contaminations as possible, whichsimultaneously is gentle on adjacent, non-contaminated areas.

Another device for purifying metals after their processing with hightemperatures is known from WO 97/12081 A1, where the insulating layerwhich surrounds the end of the electrode consists of polyether ehterketone, so that burning of the insulating layer by undesired highcurrents between the electrode and the work piece is avoided.

U.S. Pat. No. 6,315,885 B1shows a further method for electro-chemicallycleaning work pieces, in which the electorlyte used is set intovibrations in the ultrasonic range and, thus, the cleaning effect isimproved. There, cleaning is carried out in a cleaning container byimmersing the work piece in the electrolyte. This method is particularlycomplex and not suitable for big work pieces, such as, e.g., parts ofcar bodies.

Furthermore, DE 33 43 396 A1describes a method for decontaminatingmetallic components of a nuclear-technical plant, wherein anelectrolyte-liquid filled trough-shaped electrode is moved along thecomponent to be cleaned. The invention is based on the object ofproducing as low amounts as possible of waste to be removed which isachieved by guiding the electrolyte in circulation via a filter. Nodetails are given regarding the actual design of the electrode, exceptfor the enclosing of a sponge body filled with the electrolyte liquid.

Moreover, the known electrochemical cleaning methods all share thedisadvantage that the duration of the cleaning procedure for an optimumcleaning effect is relatively long.

The present invention therefore has as its object to provide anelectro-chemical cleaning method as set out above, by which an improvedcleaning effect, on the one hand, and an acceleration of the cleaningprocedure, on the other hand is obtained, while at the same time thewear of the electrode is as slight as possible.

A further object of the invention consists in providing an initiallydefined electrode for electro-chemically cleaning metal surfaces, withwhich an improved cleaning effect with a simultaneous acceleration ofthe cleaning procedure and as low a wear of the electrode as possiblecan be obtained.

Disadvantages of known cleaning processes, or of cleaning electrodes,respectively, are to be avoided, or at least reduced, respectively.

With a view to process technology, the object according to the inventionis achieved in that during the cleaning procedure, the electrode is setinto vibrations with frequencies preferably in the ultrasonic range. Bythe vibration-caused mechanical effect on the electrode, or thetransmission of the vibration from the electrode to the electrolyte and,thus, to the metal surface, a substantial acceleration of the cleaningprocedure and an improvement in the cleaning effect are attained. By theelectrolyte-provided insulating layer being arranged between theelectrode and the surface of the work piece, there is no directmechanical action of the electrode surface on the metal surface and,thus, no undesired damaging of the metal surface.

If the electrode is set into vibrations in the frequency range of morethan 20 kHz, preferably between 100 kHz and 2 MHz, optimum results canbe achieved while at the same time the expenditures for producing thevibrations are kept low.

Advantages can, moreover, be obtained in that the vibration amplitudecan be changed. Thus, by changing the vibration amplitude, e.g. bychanging the supply voltage of an electromagnetic or piezo-electricvibration generator, the cleaning effect can be manually orautomatically adapted to the respective conditions, such as, e.g., thedegree of contamination.

The object according to the invention is also achieved by an electrodefor electro-chemically cleaning surfaces of metallic work pieces, inparticular surfaces in the region of welded seams, with a terminal forconnection to an electric voltage source and an insulating layer to beimpregnated with an electrolyte, in which a means of generating avibration is provided. By this vibration generating means, the cleaningeffect is substantially improved and an acceleration of the cleaningprocedure is achieved without increasing the wear of the electrode.

The vibration generating means preferably is formed by an ultrasonicsgenerator. Such vibration generating means are comparativelycost-effective and robust. Moreover, with ultrasonics generators suchas, e.g., piezo crystals, an optimum result can be provided.

The vibration generating means may be arranged directly within theelectrode, it may form part of the electrode, or it may be externallyfastened to the electrode. The last-mentioned embodiment is particularlywell suited for retrofitting of existing electrodes.

According to a further feature of the invention, a handle is providedwhich is mounted in a vibration-damping manner or which is provided witha vibration-damping layer. In this way, comfortable handling of thecleaning electrode is attainable, since the vibrations emanating fromthe vibration generating means are not transmitted to the hand of theoperator or only a very slight part thereof is transmitted,respectively. Various elastic materials, in particular plastics with anenergy-absorbing effect, may be used.

In addition to the present insulating layer, a layer of an elasticmaterial may be provided which prevents the direct contact between theelectrode surface and the work piece, and thus is gentle on theelectrode and also on the work piece surface.

If a layer of carbon is provided, the voltage losses and the wear of theelectrode can be minimized. By this, an increased performance for thecleaning process proper is achieved. Instead of a carbon coating, alsoother coatings of special materials may be provided on the electrode,whereby the wear of the electrode can be reduced.

The insulating layer to be impregnated with the electrolyte preferablyis made of a fabric, such as, e.g., fiberglass fabric. The insulatinglayer must be porous so that an absorption of a liquid or pastyelectrolyte is possible.

Alternatively, the insulating layer may also be formed by nodules or thelike made of plastics, by which the electrode surface is kept at a safeand defined distance from the work piece surface and between which aspace for introducing a liquid or pasty electrolyte for forming anelectro-chemical cell remains clear. The nodules or the like made ofplastics may be glued to the electrode surface or applied to theelectrode surface e.g. via a carrier fabric.

Preferably, a feed line for delivering the electrolyte is provided sothat electrolyte can be delivered to the electrode continuously and,thus, the cleaning process can be carried out without interruptions.

The feed line may also include a means for metering the electrolyte, sothat an automatic or manual adaptation of the supplied electrolyteamount to the respective conditions, such as, e.g., the degree ofcontamination, can be effected.

Moreover, at least one further line may be provided for deliveringadditional components to the electrolyte. However, such mixing of theelectrolyte with additional components may also occur before the formeris delivered, so that only one line will be required for delivery of theelectrolyte.

The present invention will now be explained in more detail by way of theaccompanying drawings which show different exemplary embodiments of theinvention.

Therein:

FIG. 1 shows a sketch of the principle of an electrode forelectro-chemically cleaning surfaces of metallic work pieces;

FIG. 2 shows a cross-section through an electrode for electro-chemicallycleaning surfaces of metallic work pieces according to one embodiment ofthe invention;

FIGS. 3 to 5 show further embodiments of the invention;

FIG. 6 shows a detail of an electrode with an insulating layer in theform of plastics nodules, which electrode rests on a work piece; and

FIG. 7 shows a schematic cross-sectional view of a cleaning electrodeprovided with a handle.

FIG. 1 shows a sketch of a principle of an electrode 1 forelectro-chemically cleaning surfaces of metallic work pieces 2. Betweenthe work piece 2 and the metallic electrode body 3, a voltage source 5is connected via appropriate lines 4. The line 4 starting from theelectrode body 4 may be arranged within a connecting piece 6 forconnecting the electrode body 3 with a handle. The electrode body 3 ofthe electrode 1 is at least partially enveloped by an insulating layer7. By this insulating layer 7, which may, e.g., be formed by afiberglass fabric, a short-circuit between the electrode body 3 and thesurface of the metallic work piece 2 will be prevented. To form anelectrochemical cell, the insulating layer 7 is impregnated with asuitable electrolyte 8, e.g. a polyphosphoric acid solution.Subsequently, the electrode 1 is placed upon the work piece 2 at thecontaminated sites thereof and moved. The contaminations areelectro-chemically removed, and the surface of the work piece 2 islargely spared. Such a cleaning procedure, however, is relatively longdue to a frequent repeating of the cleaning procedure and theimpregnating of the insulating layer 7 in the electrolyte 8.

FIG. 2 shows one embodiment of an electrode 1 according to the inventionin cross-section. Within the electrode body 3, a means 9 for generatinga vibration, e.g. an ultrasonics generating means, is installed. Thevibration generating means 9 is supplied with electric energy viaappropriate connecting cables 10. The connecting cables 10 as well asthe connecting line 4 for a connection to an electric voltage source inthe respective connecting piece 6 may be provided to extend to apossibly present handle. By the vibration generating means 9, theelectrode 1 is set into vibration, in particular an ultrasonicvibration, which accelerates and assists in the cleaning procedure.

According to FIG. 3, the vibration generating means 9 may also bearranged on the electrode body 3 of the electrode 1, thereby enablingretrofitting of existing cleaning electrodes 1, e.g.

FIG. 4 shows a further embodiment of an electrode 1, in which a part ofthe electrode body 3 is formed by the vibration generating means 9.

In the variant embodiment according to FIG. 5, a layer 11 is arrangedbetween the electrode body 3 of the electrode 1 and the insulating layer7, which layer 11 may, e.g., consist of an elastic material and protectsthe surface of the electrode 1 as well as the surface of the work piece2 against direct effects of the vibration generating means 9, e.g., ifthe insulating layer 7 is damaged.

FIG. 7 shows an electrode 1 which is connected to a handle 12 via aconnecting piece 6. To prevent vibrations emanating from the vibrationgenerating means 9 from being transmitted to the handle 12, the handle12 is mounted in a vibration-dampening manner by a vibration-dampinglayer 13 being arranged between the handle 12 and the connecting piece6. At the rear end of the handle 12, the connecting lines 4, 10 for theelectrode body 3 and the vibration generating means 9 emerge. Likewise,a duct 15 for delivering the electrolyte 8 to the insulating layer 7 maybe arranged passing through the handle 12, the connecting piece 6, andthe electrode body 3.

The detail according to FIG. 6 shows a part of the surface of theelectrode body 3 and the surface of the work piece 2. In this variantembodiment, the insulating layer 7 is formed of nodules 14 or the likeof plastics, between which nodules the electrolyte can be accommodated.This is an alternative embodiment of the insulating layer 7, like thefabric layers frequently used.

The present invention is not restricted to the illustrated embodimentsof the electrodes 1. In particular, various means 9 for generating avibration may be arranged in the electrode 1 or placed thereon.

1. An electro-chemical method for cleaning the surfaces of metallic workpieces, in particular the surfaces in the region of welded seams, byusing an electrode, wherein an insulating layer is arranged between theelectrode and the work piece, and a voltage is applied between the workpiece and the electrode and the insulating layer is impregnated with anelectrolyte, wherein during the cleaning procedure, the electrode is setinto vibrations with frequencies preferably in the ultrasonic range. 2.A cleaning method according to claim 1, wherein the electrode is setinto vibrations in the frequency range of more than 20 kHz, preferablybetween 100 kHz and 2 MHz.
 3. A cleaning method according to claim 1,wherein the vibration amplitude is changed.
 4. An electrode (1) forelectro-chemically cleaning the surfaces of metallic work pieces (2), inparticular the surfaces in the region of welded seams, with a connectingterminal (4) for connection to an electric voltage source (5) and aninsulating layer (7) to be impregnated with an electrolyte (8), whereina means (9) for generating a vibration is provided.
 5. A cleaningelectrode according to claim 4, wherein the vibration generating means(9) is formed by an ultrasonics generator.
 6. A cleaning electrodeaccording to claim 4, wherein the vibration generating means (9) isarranged in the electrode (1).
 7. A cleaning electrode according toclaim 4, wherein the vibration generating means (9) forms part of theelectrode (1).
 8. A cleaning electrode according to claim 4, wherein thevibration generating means (9) is fastened to the electrode (1).
 9. Acleaning electrode according to claim 4, wherein a handle (12) isprovided which is mounted in a vibration-damping manner or which isprovided with a vibration-damping layer (13).
 10. A cleaning electrodeaccording to claim 4, wherein a layer (11) of elastic material isprovided.
 11. A cleaning electrode according to claim 4, wherein a layerof carbon is provided.
 12. A cleaning electrode according to claim 4,wherein the insulating layer (7) is formed of a fabric, preferably afiberglass fabric.
 13. A cleaning electrode according to claim 4,wherein the insulating layer (7) is formed of nodules (14) or the likeof plastics.
 14. A cleaning electrode according to claim 4, wherein aline (15) for delivering the electrolyte (8) is provided.
 15. A cleaningelectrode according to claim 10, wherein the feed line (15) contains ameans for metering the electrolyte (8).
 16. A cleaning electrodeaccording to claim 10, wherein a line for delivering additionalcomponents to the electrolyte (8) is provided.